1. Field of the Invention
The present invention generally relates to mechanical tools used to strip wires, cables, etc., and more particularly to an improved blade design for a tool used to strip the protective layers away from a group of optical fibers joined in a ribbon.
2. Description of the Prior Art
Stripping tools are well-known in the art, such as the wire strippers commonly used to remove the insulative plastic layer away from copper wires. Exemplary strippers are shown in U.S. Pat. Nos. 3,827,317 and 4,271,729. Stripping of the outer insulative layer is often required to allow electrical connection of the wire to other conductors, or to attach the terminal end of the wire to an electrical connector. Similarly, it is often necessary to strip the outer coating from an optical fiber (such as is used in telecommunications) prior to a connection or splice operation on the fiber.
In this regard, it is helpful to understand the construction of a typical optical fiber. The light signal travels within the innermost core of the fiber, usually made of glass (silica), although a polymer is sometimes used. The core is surrounded by a cladding, typically formed from the same material as the core (silica), although it is doped differently to provide a lower refractive index (resulting in internal reflection of most of the light within the core). The cladding is further surrounded by a buffer coating to protect the fiber from adverse external effects. The buffer coating is typically formed from a UV-cured polymeric material.
To prepare a fiber for a connector or splice, it is necessary to strip away the buffer coating, but without damaging the cladding layer. This operation can be very difficult due to the small dimensions involved and the ease with which the glass cladding can be nicked. For example, most optical fibers used in data communications have an outer (cladding) diameter of 125 .mu.m and a buffer diameter of 250 .mu.m. The core diameter varies depending upon application, e.g., a single-mode fiber may have a 10 .mu.m core diameter and a multimode fiber may have up to an 85 .mu.m core diameter.
The tools illustrated in the above-mentioned patents have been modified for use in stripping optical fibers, but still possess certain disadvantages due to the fact that the stripping operation is critical in at least two respects. First of all, if the stripping tool digs too far into the buffered fiber (or the fiber is improperly aligned with the blades of the tool), it will damage the cladding, possibly breaking the fiber, or at least decreasing the tensile strength of the fiber. Secondly, if the blades do not cut deep enough, then the buffer coating may not be fully stripped, which can lead to later problems such as misalignment in a splice or inability to insert the fiber into a connector ferrule.
Techniques have been devised to minimize the foregoing deficiencies, such as improved manufacture of the stripper blades, as discussed in U.S. Pat. No. 4,315,444. These problems still remain, however, and are especially pronounced when simultaneously stripping a plurality of fibers which have been formed into a flat ribbon. Such a fiber ribbon typically includes (in addition to the core, cladding and buffer layers of each fiber) an outer protective coating, such as a polyester film or tape, which is bonded to the fibers, typically with an acrylic adhesive. Other ribbons provide a UV curable polymeric matrix which bonds or encapsulates the fibers. Therefore, in addition to removing buffer coating, the stripping tool must also remove the outer bonding material.
The tools described in the above-mentioned patents have further been modified for use in stripping fiber ribbons, as demonstrated in U.S. Pat. No. 4,850,108. This prior art stripper and its components are shown in FIGS. 1-4, and are discussed more fully below in the detailed description of the preferred embodiment. The closest prior art blade design is illustrated in FIG. 4, along with a cross-sectional view of the fiber ribbon. FIG. 4 serves to illustrate the additional problem that, even with the relatively tight tolerances provided for ribbon alignment, the ribbon may still be misaligned prior to stripping, with the likely result that one or more of the individual fibers will become damaged. An alternative prior art "flat" blade design, having no semicircular cutouts, does not require any alignment at all, but is not suited to stripping ribbons wherein the fibers are interposed between two polyester films. Such a ribbon construction in found in the ASR ribbon sold by American Telephone & Telegraph Co. Flat blade designs do not strip this type of ribbon well, as the straight blade edge cannot easily puncture the outer tape. It would, therefore, be desirable and advantageous to devise a blade design for a fiber ribbon stripping tool which can easily strip such ribbons, and further which would minimize or eliminate misalignments, as well as safeguard against overstripping, i.e., cutting into the fiber cladding or core.